Rotary machines, in which at least one rotor has planetary motion within a housing, can be employed, for example, as rotary compressors, pumps (including positive displacement pumps, dynamic pumps and vacuum pumps) or expansion engines.
Conventional rotary machines can have one or more rotors. Various shapes of rotors are known, including circular, elliptical, triangular and, in some cases, the rotors incorporate vanes. Vanes can be mounted on a rotor in a housing, and can be of variable length or urged to maintain contact with the interior surface of the housing as the rotor rotates. The housing for the rotor is most commonly cylindrical although other housing shapes such as trochoidal (either hypo- or epitrochoidal) shapes are known. There is a class of rotary machines for which the rotor is trochoidal and the housing is also trochoidal, wherein the housing has one more apex than the rotor. Trochoidal shapes can be generated by tracing a point on the circumference of a first circle as it is rolled around the circumference of a second circle either on the inside (producing a hypotrochoidal shape) or outside (producing an epitrochoidal shape).
A configuration in which the housing (or an outer rotor) has one more apex (or tooth) than the inner rotor is known as a generated rotor or gerotor. A gerotor is a positive displacement pump and can comprise a trochoidal inner rotor and an outer rotor formed by a circle with intersecting arcs.
Various gerotor configurations can be designed by rotating an inner rotor about a first point moving in a circle about a second point wherein the second point is fixed. The inner rotor can comprise two or more apexes, and can rotate in the same direction or in the opposite direction as the rotation of the first point about the second point. The relative rotational rates of the rotor and the first point about the second point can be adjusted to achieve a desired gerotor configuration.
Rotary pumps are known devices that can move a fluid from one place to another. There is a wide range of end uses for rotary pumps including irrigation, fire-fighting, flood control, water supply, gasoline supply, refrigeration, chemical movement and sewage transfer.
Rotary pumps are typically positive displacement pumps comprising a fixed housing, gears, cams, rotors, vanes and similar elements. Rotary pumps usually have close running clearances, do not require suction or discharge valves, and are often lubricated only by the fluid being pumped.
A positive displacement pump moves the fluid by trapping a volume of fluid and forcing the trapped volume into a discharge pipe. Some positive displacement pumps employ an expanding cavity on the suction side and a decreasing cavity on the discharge side. Fluid flows into the pump as the cavity on the suction side expands and the fluid flows out of the discharge pipe as the cavity collapses. The output volume is the same for each cycle of operation. Theoretically, a positive displacement pump can produce the same flow rate at a given pump speed regardless of the discharge pressure.
A rotodynamic pump is a kinetic machine in which energy is imparted continuously to the fluid by means of a rotating impeller, propeller, or rotor.
Rotary machines, such as those described above, can be designed for various applications. The design and configuration of rotary machines can offer particular advantages for certain applications. For example, rotary pumps, such as those described above, can be designed for various applications with suitable capacity and discharge pressure. The design and configuration of rotary pumps can offer particular advantages, such as high volumetric efficiency, for certain applications.